The present invention relates to a light source apparatus for selecting or separating light having a required wavelength from light emitted from a single light source or a plurality of light sources and projecting the light. More particularly, the present invention relates to a light source apparatus used for obtaining information of a measured object based on the intensity of transmitted light or reflected light (including scattered light) obtained by irradiating the measured object with visible light or near-infrared light.
In recent years, various kinds of optical measurements have been performed using light transmitted through, reflected by, or scattered by, a measured object. In performing such an optical measurement, the intensity of transmitted light, reflected light, or scattered light, obtained by irradiating a measured object with light is detected, thereby obtaining information of the measured object.
Light having a preferred wavelength suitable for the measured object is selected as the light used for the measurement. On the other hand, even when the measurement is performed with respect to the same measured object, the intensity of the resulting transmitted light, reflected light, or scattered light, differs depending upon the wavelength selected for the measurement. Thus, a preferred wavelength must be selected in consideration of the measurement conditions. In order to realize highly sensitive measurement, it is necessary to project light including a light beam having the wavelength thus selected onto the measured object with high precision.
In performing such an optical measurement, a light source apparatus including a combination of at least one light source emitting light having a plurality of wavelengths and a plurality of filters having respectively different transmission wavelengths has conventionally been used. In such a conventional light source apparatus, a plurality of filters are movably provided. Depending on a wavelength used for measurement, one of the plurality of filters is selected and then moved to a position suitable for receiving a light emitted from the light source, including light with the required wavelength, thereby projecting the light beam with the wavelength used for measurement onto a measured object.
However, in such a conventional light source apparatus, in order to sequentially change the wavelengths of the light beams to be incident onto the same measured object (i.e., in order to perform a scanning of the wavelengths), the plurality of filters are required to be sequentially interchanged by mechanically moving a filter unit. Thus, such a conventional apparatus has a problem in that the configuration and the operation of the entire apparatus becomes complicated or the size thereof becomes large.
In addition, in a conventional light source apparatus, the quantity of light adversely becomes unstable depending upon the ambient temperature around the light source. Moreover, in the case where such a light source apparatus includes a plurality of light sources, every time a light source emitting light with the wavelength used for measurement is selected from the plurality of light sources, the power supplies of the light source are required to be turned ON/OFF. Thus, every time light sources are switched, it takes a significant period of time until the quantity of light is stabilized. Furthermore, since the light sources themselves have respectively different wavelength characteristics and a plurality of filters are used, the intensity of light emitted from the conventional light source apparatus varies depending on the wavelength thereof.
Furthermore, light which has been incident on the measured object and then transmitted through, reflected by or scattered by the measured object is used for performing the above-described optical measurement. Thus, the intensity of the light used for measurement is affected by the absorption of light by the measured object.
An exemplary relationship between the intensity I0(xcex) of the light irradiated onto the measured object and the intensity I(xcex) of the light transmitted through the measured object is shown in FIG. 7. As shown in FIG. 7, because the light has been absorbed by the measured object, the light intensity greatly differs between the incident light and the light used for measurement (in this case, the transmitted light). Therefore, in order to maximize the measurement resolution, the sensitivity of a light-receiving system is required to be varied in accordance with the intensity of the light used for measurement.
The present invention has been made in view of the above-mentioned circumstances and has objectives of providing a stable light source apparatus which can project a light beam having a wavelength required for measurement onto a measured object with high precision and also can eliminate the variation in the emission intensities with respect to the wavelengths, and providing a light source apparatus which can be operated easily and can be downsized.
The light source apparatus of this invention includes a light source section for emitting light having a plurality of wavelengths and a filter for selecting light having a single wavelength from the light having the plurality of wavelengths, and for separately outputting light having the selected wavelength, the selected wavelength being electrically variable, thereby realizing the above objectives.
An intensity of the light having the selected wavelength may be electrically variable.
The filter may be an acousto-optic tunable filter.
The filter may output the light having the selected wavelength in a direction different from directions in which remaining light having other wavelengths is output.
The filter may output the light having the selected wavelength as plus and minus first-order light beams and the remaining light as a zero-order light beam.
The light source apparatus may further include a combining member for combining the plus and minus first-order light beams into a single light beam.
The filter may output the light having the selected wavelength as xc2x1m order light beams and the remaining light as a zero-order light beam, where m is an integer larger than 2.
The light source apparatus may further include a combining member for combining xc2x1m order light beams into a single light beam.
The light source section may include a plurality of light sources.
The light source section may include a single light source.
The light source apparatus may further include a converging member for converging the light output from the filter.
The light source apparatus may further include a member for allowing the light having the selected wavelength to pass therethrough and blocking the other light.
The filter may be electrically adjusted such that the selected wavelength is sequentially varied while an intensity of the light having the selected wavelength is constant.
The filter may be electrically adjusted such that an intensity of the light having the selected wavelength is sequentially varied while the selected wavelength is constant.
The light source section may include laser diodes.
The light source section may include light-emitting diodes.
The plurality of light sources may emit a plurality of light beams having respectively different wavelength ranges.
The plurality of light sources may be arranged in an array.
The light source apparatus may further include a lens array which is provided between the light source section and the filter and has a plurality of lenses.
The measurement method of the invention uses light emitted from a light source apparatus which includes: a light source section for emitting light having a plurality of wavelengths; and a filter for selecting light having a single wavelength from the light having the plurality of wavelengths, and for separately outputting light having the selected wavelength, the selected wavelength being electrically variable. The method includes the steps of: irradiating a measured object with the light emitted from the light source apparatus; receiving light transmitted through, reflected by, or scattered, by the measured object; and performing a measurement with respect to the measured object based on the received light. In the irradiation step, at least one of the selected wavelength and an intensity of the light having the selected wavelength is sequentially varied, thereby realizing the above objectives.
Another measurement method of the invention uses light emitted from a light source apparatus which includes: a light source section for emitting light having a plurality of wavelengths; and a filter for selecting light having a single wavelength from the light having the plurality of wavelengths, and for separately outputting light having the selected wavelength, the selected wavelength being electrically variable. The method includes the steps of: irradiating a measured object with the light emitted from the light source apparatus; receiving light transmitted through, reflected by, or scattered by, the measured object as light for measurement; and performing a measurement with respect to the measured object based on the light for measurement. The method further includes a step of electrically adjusting the filter such that an intensity of the light for measurement becomes substantially constant without depending upon the selected wavelength, prior to the irradiation step, thereby realizing the above objectives.